Method for the production or restoration of working rolls for hot rolling of metallic flat products

ABSTRACT

The invention relates to a method for the production or restoration of working rolls for hot rolling metallic flat products, in particular for shaping steel slabs to pre-strips on broad strip mills, wherein the improvement resides in that the central circumferential zone of the roll body is provided with a greater coarseness than the two marginal zones. With this process it is possible to employ rolls with great hardness and yet obtain an excellent roll bite, so that the efficiency is greatly enhanced.

United States Patent Krausz et al.

[54] METHOD FOR THE PRODUCTION OR RESTORATION OF WORKING ROLLS FOR HOT ROLLING OF METALLIC FLAT PRODUCTS [72] Inventors: Johann Krausz; Johan Feichtinger,

both of Linz, Austria [73] Assignee: Vereinigte Osterreichische Eisen-und Stahlwerke Aktiengesellschaft, Linz, Austria 22 Filed: Dec.23, 1970 [21] Appl.No.: l0l,077

[30] Foreign Application Priority Data Dec. 24, 1969 Austria ..12039/69 [52] US. Cl ..5l/326, 51/289 R, 51/319 [51] Int. Cl. B24b H00 [58] Field of Search ..51/326,-49, 289 R, 319, 320,

[451 Nov. 21, 1972 [56] References Cited UNITED STATES PATENTS 1,697,810 1/1929 Comstock; ..5l/3l9 X 1,743,623 H1930 Ross ..5 H320 3,089,293 5/1963 Hoier et al ..5 H49 X Primary Examiner-Lester M. Swingle Attorney-Brumbaugh,Graves, Donohue & Raymond [57] 1 ABSTRACT The invention relates to a method for the production or restoration of working rolls for hot rolling metallic flat products, in particular for shaping steel slabs to pre-strips on broad strip mills, wherein the improvement resides in that the central circumferential zone of the roll body is provided with a greater coarseness than the two marginal zones. With this process it is possible to employ rolls with great hardness and yet obtain an excellent roll bite, so that the efficiency is greatly enhanced.

4 Claims, 3 Drawing Figures METHOD. FOR THE PRODUCTION OR RESTORATION OF- WORKING ROLLS FOR HOT ROLLING OF METALLIC FLAT PRODUCTS The invention relates to a method for the production or restoration of working rolls for hot rolling of metallic flat products, in particular for shaping steel slabs to pre-strips on broad strip mills.

In general the roll body of the working rolls is desired to be as hard as possible so as to prolong the life of the rolls expressed in metric tons throughput mrn abrasion or to keep small the necessary abrasion or grinding for restoring the original roll profile. However,

the friction angle of the rollis impairedwith increasing hardness so that the bite of the rolls is deteriorated and the electrical power of the roll stand cannot be fully exploited, i.e., the full rolling capacity cannot be reached. When harder rolls are used also the number of passes is greater and when the rolls slip through shocks may be exerted on the drive, particularly on the spindle couplings. Owing to the higher number of passes only lighter slabs may be inserted so that when strips are produced in the broad strip mill arranged in succession to the rolling stand coils of relatively low weight are obtained. When the wear of the working rolls has reached a certain degree, the original roll profile will have to be restored by grinding the entire body surface, which process is repeated at specific time intervals. Experience has shown that the center area of the working rolls is worn to a greater degree than the marginal areas when flat products are rolled; when a certain degree of wear is reached broad sheets or strips can no longer be rolled; then the rolls have to be removed and reground.

The invention is aimed at improving the operating conditions at hot rolling stands and at creating a method for the production or restoration of working rolls by which the described disadvantages and difficulti es may be eliminated or reduced.

The invention resides in that the central circumferential zone of the roll body is provided with a greater coarseness than the two marginal zones of the roll body.

The length of the central circumferential zone which is provided with a greater coarseness may amount to from about 1/5 to 1$ of the overall body length.

In the production of new working rolls the central circumferential zone may artificially be roughened e.g. by means of sand jets.

When the original profile of the working rolls is restored, the rolls are suitably re-ground only in the area of the marginal zones while the natural coarseness produced by the rolling process in the area of the central circumferential zone is retained.

The preferred application field for rolls produced or restored according to the invention is in shaping steel slabs to pre-strips for broad strip mills.

In order that details of the invention and its advantages may be more fully understood an embodiment thereof shall now. be explained with reference to the accompanying drawing.

FIG. 1 is a schematical representation of a pair of working rolls in which the wear occurring in the course of rolling is illustrated on an excessive scale.

FIG. 2 is a longitudinal sectional view of a removed working roll prior to re-grinding, the surface layer being shown on enlarged scale.

FIG. 3*is a similar representation as FIG. 2 showing a roll re-groundaccording to the invention.

When slabs, are rolled to pre-strips the rolling program is scheduled in a manner that at first the broad slabs and then gradually the narrower slabs are rolled. After a specific throughput the profile of the working rolls A- changes approximately as-shown in FIG. 1: The marginal zones 1 are worn to a very small degree while the center area 2' is greatly, worn. As soon as this condition is reached, the working rolls have to be removed and abraded. FIG. 2 shows the surface contour of a removed working roll; the contour is established by means of a testing device for ascertaining the coarseness. The height of the illustrated zig-zag lines, the amplitudes, is a measure for the coarseness; for better clarity, the amplitudes areshown on an enlarged scale, the lines of the screen on the left hand side of FIGS. 2 and 3 indicating a distance of 0.05 mm. v

According to the invention the central area 2 of the rolls is provided with greater coarseness than the marginal zones 1. The body length of the roll on which the measurements were carried out, amounted to 2,240 mm'and the diameter D to 895.01 mm, the roll camber being 0.1 mm. The maximum wear depth in the central area of the roll amounted to about 0.23 mm. The contour of the original roll profile is denoted with 3. FIG. 3 shows the roll profile of a roll that has been re-ground according to the invention. As proposed by the invention not the entire body surface was re-ground; instead, the coarseness obtained by rolling was maintained in the zone 2 in the middle part of the roll having a length L and only the marginal zones 1 were re-ground in customary manner. Thus, the biting capacity of the working rolls is essentially improved. The marginal zones denoted with I in FIG. 1 thus were adapted to the central zone 2 by means of grinding. The contours of the ground rolling profile are denotedwith numeral 1 in FIG. 3. This re-ground roll had a diameter D, of 894.54 mm, the roll abrasion (reduction of diameter) at the marginal zones 1 amounting to 0.47 mm. For a comparison with the conventional operation method, in FIG. 3 the diameter D, is indicated, to which the rolls had been ground so far, both in the marginal zones and in the central zone. The diameter D,- corresponds to an abrasion of about 0.57 to 0.67mm over the entire body length; in the earlier method a certain subjective inaccuracy had been unavoidable. With rolls having a body length of from 2.2 to 2.7 m the length of the zone L amounts to 500 to 800 mm.

When working rolls with a greater coarseness in the central area were used for operation in a four-high stand for rolling steel slabs to pre-strips for a broad strip mill the following advantages were obtained: it was possible to increase the efficiency of the working rolls in metric tons throughput mm abrasion from 3,800 to 5,700 so that the consumption of working rolls was lowered by one third. Owing to the improved bite the number of passes was reduced from 7 to 5, so that the throughput capacity of the break-down stand and the broad strip mill was increased by about 8 percent. The rolling stand could be operated with full power so that without increasing the number of passes the thickness of the slabs was increased from originally mm. to 210 mm; thus also the weight of the rolling coils was increased. The working time for grinding a roll was reduced from 6 to 4 hours. The texture of the surface of the hot coils produced on the broad strip mill by rolling the pre-strips was not influenced. it has been shown that the use of hard working rolls, which are not ground 1 over the entire body length, does not entail any disadvantages.

The invention is also applicable with four-high rolling stands for the production of plates.

Experience has shown that when factory-new rolls are built into a stand, only after a certain throughput their coarseness is sufficient to improve the bite. in order to gain the full advantage of the invention also with fresh rolls the central zone may be coarsened artificially already during production for example by sand blasting; the operating conditions in a rolling stand may then be improved during the whole life of the working having a predetermined length and two ends, comprising providing a prespecified central circumferential zone of said roll with a greater roughness than two predetermined marginal zones. Y

2. The method set forth in claim 1, wherein the central' circumferential zone comprises from 1/5 to 1/3 of the length of the working roll.

3. The method set forth in claim 1 for preparing a new working roll, wherein the central circumferential zone is roughened by sandblasting.

4. The method set forth in claim 1 for preparing a previously used working roll which has been roughened substantially over its entire surface by previous rolling operations, wherein the original profile of the working roll is restored by grinding the roll body at said marginal zones while retaining the natural roughness produced in the previous rolling operations in said central circumferential zone. 

1. A method of preparing a working roll for hot rolling mills, the roll being substantially cylindrical and having a predetermined length and two ends, comprising providing a prespecified central circumferential zone of said roll with a greater roughness than two predetermined marginal zones.
 1. A method of preparing a working roll for hot rolling mills, the roll being substantially cylindrical and having a predetermined length and two ends, comprising providing a prespecified central circumferential zone of said roll with a greater roughness than two predetermined marginal zones.
 2. The method set forth in claim 1, wherein the central circumferential zone comprises from 1/5 to 1/3 of the length of the working roll.
 3. The method set forth in claim 1 for preparing a new working roll, wherein the central circumferential zone is roughened by sandblasting. 